Stabilization of thermally unstable dmt with bhet

ABSTRACT

Disclosed is the stabilization of thermally unstable dimethyl terephthalate with a stabilizing quantity of bis( Beta hydroxyethyl)terephthalate.

United States Patent [1 1 Mori et al.

[ June 26, 1973 STABILIZATION OF THERMALLY UNSTABLE DMT WITH BI-IETInventors: Hiroshi Mori; Michio Yamamoto;

Koshi Namie; Teruhisa Kimoto, all of Maisuyama, Japan Assignee: TeijinHercules Chemical Company Limited, Tokyo, Japan Filed: Jan. 8 1971 Appl.No.: 105,071

US. Cl 260/475 B Int. Cl. C07c 69/82 Field of Search 260/475 B, 475 PRPrimary Examiner-Lorraine A. Weinberger Assistant ExaminerE. Jane SkellyAttorney-George l-l. Hopkins [57] ABSTRACT Disclosed is thestabilization of thermally unstable dimethyl terephthalate with astabilizing quantity of bis(- B-hydroxyethyl)terephthalate.

' 3 Claims, No Drawings STABILIZATION OF THERMALLY UNSTABLE DMT WITHBHET This invention is in the chemical arts. It has to do with thatbranch of organic chemistry pertaining to alcohol esters of aromaticdicarboxylic acids.

Dimethyl terephthalate (DMT) is a well known normally solid chemical ofcommercial importance. It is used in large quantities in the productionof polyesters from which fibers and the like are made.

Recently, it has become common practice to ship and store DMT in themolten state, that is, at temperatures above 140C. In some instances,however, DMT is unstable to the extent that under such conditions itscolor tends to increase substantially. As a result, the polyester madefrom it is off-color and sometimes has a degree of polymerization lowerthan that which is desired. The problem to which this invention providesa solution is how to stabilize thermally unstable DMT.

In summary, this invention comprises a thermally stable compositionconsisting essentially of thermally unstable DMT and dispersed thereinat a stabilizing concentration material (hereinafter referred to asstabilizing material) consisting essentially ofbis(B-hydroxyethyl)terephthalate (BHET).

BHET is an intermediate formed in the production of highly polymericpolyesters from DMT and ethylene glycol. In the process generallyemployed for such production, ester exchange reaction of DMT andethylene glycol is effected with a catalyst to give a reaction mixtureconsisting essentially of BHET. Methanol formed in the reaction usuallyvolatilizes from the reaction mixture and normally is recovered. Thereaction mixture thus obtained generally not only comprises BHET as itspredominant component, but also, catalyst and one or more condensates ofBHET, such as the dimer, trimer, tetramer, and the like of BHET. Thisreaction mixture is hereinafter referred to as DGT. Subsequently, DGT issubjectedto a condensation reaction to form the highly polymericpolyester, which reaction, depending on the catalyst employed in thereaction of DMT with ethylene glycol, is effected either with thatcatalyst or another catalyst.

In one embodiment of this inventionthe stabilizing material comprisesBHET alone.

In another embodiment of this invention the stabilizing materialcomprises DGT.

In still another embodiment of this invention, the stabilizing materialcomprises DGT plus one or more stabilizers for the ultimate polyester,which stabilizer or stabilizers are at a total concentration usuallyless than percent by weight of the DGT.

Concentration of the stabilizing material in the thermally stabilizedDMT of this invention is in a wide range. However, satisfactory resultsare obtained when the concentration of the stabilizing material issubstantially 0.1-5 percent by weight of the thermally unstable DMT.

The composition of this invention is made several ways.

In one procedure it is made by admixing the stabilizing material aloneor with other additives with the thermally unstable DMT in the moltenstate. This admixing can be performed by adding the stabilizing materialwhile stirring the molten DMT. It also can be done by blowing with aninert gas the stabilizing material into the molten DMT. The resultingmolten composition can be maintained in the molten state until it isused, or it can be cooled until solid.

In another procedure the composition of this invention is made byadmixing the stabilizing material alone or with other additives with thethermally unstable DMT in the finely divided solid state. At the sametime the stabilizing material can be in the finely divided solid state,the molten state or dissolved in an inert solvent which, subsequently,if desired, is removed by evaporation. Thereafter, when the DMT ismelted for use, the stabilizing material automatically is incorporatedin it.

In still another procedure the composition of this invention is made byadmixing the stabilizing material alone or with other additives with asolution of the thermally unstable DMT in a solvent preferably for boththe DMT and the stabilizing material. Preferably, the stabilizingmaterial when added to the solution is dissolved either in a mutualsolvent or the same solvent. After the stabilizing material has beendispersed in the solution of DMT, the solvent is removed by evaporation,or crystallization of the DMT is effected. In either case the solid DMThas incorporated in it the stabilizing material of this invention.

In yet another procedure the stabilizing material is admixed with moltenDMT so that the concentration of the stabilizing material issubstantially higher than the ultimate use concentration. A stabilizingquantity of the concentrate thus formed is subsequently added to the DMTto be stabilized.

The efiicacy of the stabilizing material of this invention instabilizing thermally unstable DMT is demonstrated by the followingtabulated data obtained on samples of specific embodiments of thethermally stabilized DMT of this invention. The data were obtained bymeasuring the initial color of samples of thermally unstable DMT aloneand with the indicated additives at the noted concentrations in parts byweight per million parts by weight of DMT. The samples were thenestablished and maintained at C. for 24 hours. The color of each samplewas measured 4 hours, 10 hours and 24 hours after establishing thesample at 175C.

The foregoing data demonstrate that the thermally induced increase incoloring of thermally unstable DMT stabilized according to thisinvention is substantially lower than that of thermally unstable DMTwithout stabilizing material.

Thus, this invention provides a thermally stabilized DMT composition.

A feature of advantage of this invention is that the increase in colorof DMT stabilized according to this invention, which increase is broughtabout by high temperatures at the time of storage or transfer orconversion of it into polyester, is substantially lower than that ofunstabilized thermally unstable DMT. Consequently, polyester made fromDMT stabilized according to this invention has substantially less colorthan polyester made from the thermally unstable DMT without stabilizingmaterial.

Another feature of advantage of this invention is that when thestabilized DMT of this invention is used in the production of polyestersthe possibility of the stabilizing material adversely affecting one orboth of the polyester production reactions and the ultimate polyesterproduct is minimized, if not eliminated, because the stabilizingmaterial itself is an intermediate or intermediate product in theproduction of the polyester.

Other features, advantages and specific embodiments of this inventionwill become readily apparent to those exercising ordinary skill in theart after reading the foregoing disclosures. In this connection, whilespecific embodiments of this invention have been described inconsiderable detail, variations and modifications of these embodimentscan be effected without departing from the spirit and scope of theinvention as disclosed and claimed.

The language consisting essentially of as used in this specificationexcludes any unrecited substance at a concentration sufficient tosubstantially adversely affeet the essential properties andcharacteristics of the composition being defined, while permitting thepresence of one or more unrecited substances at concentrationsinsufficient to substantially adversely affect said essential propertiesand characteristics.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A thermally stable composition consisting essentially of thermallyunstable DMT and dispersed therein at a stabilizing concentrationmaterial consisting essentially of BHET.

2. A thermally stable composition consisting essentially of thermallyunstable DMT and dispersed therein, at about 0.1-5 percent by weight ofthe thermally unstable DMT, material consisting essentially of BHET.

3. A thermally stable composition consisting essentially of thermallyunstable DMT and dispersed therein, at about 0.1-5 percent by weight ofthe thermally unstable DMT, material consisting essentially of DMT andethylene glycol ester exchange reaction mixture.

2. A thermally stable composition consisting essentially of thermallyunstable DMT and dispersed therein, at about 0.1-5 percent by weight ofthe thermally unstable DMT, material consisting essentially of BHET. 3.A thermally stable composition consisting essentially of thermallyunstable DMT and dispersed therein, at about 0.1-5 percent by weight ofthe thermally unstable DMT, material consisting essentially of DMT andethylene glycol ester exchange reaction mixture.